The present invention relates to a pneumatic tire, more particularly to a structure of the tread portion of a heavy duty radial tire having a four or five-rib tread pattern capable of reducing uneven wear.
In the long-route highway express buses traveling under the almost full load capacity, widely used are radial tires having rib type tread patterns in view of their low fuel consumption and low noise natures.
In the case of the rib-pattern radial tires used in such long-route highway express buses, there is a problem with the front tires such that the axially outermost shoulder ribs are worn largely and rapidly when compares with the other ribs such as center rib because the center of gravity of the vehicle body is relatively high and the rolling of the vehicle body during running is relatively large, and the front tires are subjected to large lateral acceleration and further braking force during running.
In order to prevent such uneven wear and rapid wear in the shoulder ribs (hereinafter, collectively, the “shoulder wear”), a conventionally employed technique is to increase the ground pressure in the tread shoulder regions in order to lessen slippage between the shoulder ribs and road surface so that wear of the shoulder ribs are reduced.
However, this conventional technique can not fully resolve the problem of the shoulder wear occurring on the front tires of the long-route highway express buses.